Method and apparatus for starting an engine in a hybrid vehicle

ABSTRACT

A method and apparatus for starting an engine in a hybrid vehicle being driven by an electric motor is disclosed. The motor is operably configured to deliver mechanical power through an automatic transmission to at least one vehicle drive wheel to cause an acceleration of the vehicle. The method involves coupling the engine to the motor to cause an inertial load on the motor thus causing the motor to decelerate to a reduced rotational speed to provide a starting torque to the engine for starting the engine, and causing the automatic transmission to change gear ratio to a target gear ratio associated with the reduced rotational speed while causing the motor to decelerate, the motor being operable to deliver increased torque at the reduced rotational speed, thereby generally maintaining the acceleration of the vehicle.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates generally to hybrid vehicles and moreparticularly to starting an engine in a hybrid vehicle.

2. Description of Related Art

Hybrid electric vehicles having an engine (such as an internalcombustion engine) and an electric motor, for providing power to thevehicle have become a viable alternative to conventional internalcombustion engine vehicles. While such vehicles may require more complexpower transmission components, this complexity is offset by improvedfuel consumption and a corresponding reduction in pollutant emissionsfrom the engine.

Given the present climate of higher prices for fossil fuels, there is acorresponding desire to further reduce fuel consumption costs whenoperating hybrid vehicles. Hybrid electrical vehicles reduce fuelconsumption by apportioning the power required to operate the vehiclebetween the engine and electric motor, to cause these components tooperate at efficient operating points. For example, when moving slowlyor when starting off from a stationary position, the electric motor maybe considerably more efficient than the engine and in this case most ofthe power may be supplied by the motor. Engines generally operate moreefficiently at higher rotational speeds and accordingly, at highervehicle velocity a greater proportion of power may be supplied by theengine. When moving slowly, it may thus be desirable to supply all ofthe necessary operating torque from the motor, while the engine remainsstopped, thus reducing fuel consumption and emissions.

In some hybrid vehicles, the electric motor is coupled to the engine andmay be used to start the engine, thus eliminating the need for aseparate electric starter motor, as found in conventional internalcombustion engine vehicles. When the vehicle operates under conditionsthat require torque to be supplied from the engine, the motor may bemechanically coupled to the engine to provide a starting torque thereto.The diversion of torque from the vehicle wheels to the engine whilestarting the engine may result in undesirable acceleration changes.

There remains a need for improved methods and apparatus for startingengines in hybrid vehicles.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention there is provided amethod for starting an engine in a hybrid vehicle being driven by anelectric motor, the motor being operably configured to delivermechanical power through an automatic transmission to at least onevehicle drive wheel to cause an acceleration of the vehicle. The methodinvolves coupling the engine to the motor to cause an inertial load onthe motor thus causing the motor to decelerate to a reduced rotationalspeed to provide a starting torque to the engine for starting theengine, and causing the automatic transmission to change gear ratio to atarget gear ratio associated with the reduced rotational speed whilecausing the motor to decelerate, the motor being operable to deliverincreased torque at the reduced rotational speed, thereby generallymaintaining the acceleration of the vehicle.

Coupling the engine may involve coupling the engine to the motor when avehicle operating condition meets a criterion for starting the engine.

Causing the automatic transmission to change gear ratio may involvecausing the automatic transmission to change gear ratio to the targetgear ratio when the vehicle operating condition meets the criterion forstarting the engine.

Coupling the engine to the motor when the vehicle operating conditionmeets the criterion for starting the engine may involve coupling theengine to the motor when at least one of the motor speed reaches areference speed, the vehicle reaches a reference velocity, a storageelement for supplying electrical energy to the motor reaches a referenceminimum state of charge, and a voltage at which the electrical energymay be supplied to the motor reaches a reference minimum level.

Causing the engine to be mechanically coupled to the motor may involvecausing a clutch between the motor and the engine to be engaged totransmit the starting torque to the engine.

The method may involve producing a clutch control signal when a vehicleoperating condition meets a criterion for starting the engine, theclutch having a disengaged state operable to decouple the engine fromthe motor and an engaged state operable to couple the engine to themotor, and the clutch may be operably configured to change from thedisengaged state to the engaged state in response to the clutch controlsignal.

Producing the clutch control signal may involve producing a discreteclutch control signal having first and second states, the clutch beingoperably configured to change from the disengaged state to the engagedstate in response to the clutch control signal having the first state.

Producing the clutch control signal may involve producing a clutchcontrol signal having a time-varying amplitude representing a desiredamount of engagement of the clutch between the engaged state and thedisengaged state, the clutch being responsive to the clutch controlsignal to control an amount of slippage of the clutch when coupling theengine to the motor.

The method may involve producing a transmission shift signal in responseto the vehicle operating condition meeting the criterion for startingthe engine, and causing the automatic transmission to change gear ratiomay involve causing the automatic transmission to change gear ratio tothe target gear ratio in response to the transmission shift signal.

Producing the clutch control signal may involve producing the clutchcontrol signal a first time period after the vehicle operating conditionmeets the criterion for starting the engine, and producing thetransmission shift signal may involve producing the transmission shiftsignal a second time period after the vehicle operating condition meetsthe criterion for starting the engine, the first and second time periodsbeing selected such that a substantially constant acceleration of thevehicle may be maintained while starting the engine.

The method may involve producing an engine start signal in response tothe vehicle operating condition meeting the criterion for starting theengine.

Producing the engine start signal may involve producing at least one ofan ignition signal for controlling ignition of the engine, and a fuelcontrol signal for causing fuel to be supplied to the engine.

Producing the engine start signal may involve producing the engine startsignal a third time period after the vehicle operating condition meetsthe criterion for starting the engine, the third time period beingsufficient time to permit the engine to reach a rotational speed thatgenerally matches the rotational speed of the motor.

The automatic transmission may be operably configured to provide aplurality of discrete gear ratios and causing the automatic transmissionto change the gear ratio may involve causing the automatic transmissionto change gear ratio from a first gear ratio to the target gear ratio.

The automatic transmission may be operably configured to provide acontinuously variable gear ratio and causing the automatic transmissionto change the gear ratio may involve causing the automatic transmissionto change gear ratio by an amount sufficient to provide the target gearratio between the motor and the at least one drive wheel.

In accordance with another aspect of the invention there is provided anapparatus for starting an engine in a hybrid vehicle being driven by anelectric motor, the motor being operably configured to delivermechanical power through an automatic transmission to at least onevehicle drive wheel to cause an acceleration of the vehicle. Theapparatus includes provisions for coupling the engine to the motor tocause an inertial load on the motor thus causing the motor to decelerateto a reduced rotational speed to provide a starting torque to the enginefor starting the engine, and provisions for causing the automatictransmission to change gear ratio to a target gear ratio associated withthe reduced rotational speed while causing the motor to decelerate, themotor being operable to deliver increased torque at the reducedrotational speed, thereby generally maintaining the acceleration of thevehicle.

The provisions for coupling the engine may include provisions forcoupling the engine to the motor when a vehicle operating conditionmeets a criterion for starting the engine.

The provisions for causing the automatic transmission to change gearratio may include provisions for causing the automatic transmission tochange gear ratio to the target gear ratio when the vehicle operatingcondition meets the criterion for starting the engine.

The provisions for coupling the engine to the motor when the vehicleoperating condition meets the criterion for starting the engine mayinclude provisions for coupling the engine to the motor when at leastone of the motor speed reaches a reference speed, the vehicle reaches areference velocity, a storage element for supplying electrical energy tothe motor reaches a reference minimum state of charge, and a voltage atwhich the electrical energy may be supplied to the motor reaches areference minimum level.

The provisions for causing the engine to be mechanically coupled to themotor may include causing a clutch between the motor and the engine tobe engaged to transmit the starting torque to the engine.

The apparatus may include provisions for producing a clutch controlsignal when a vehicle operating condition meets a criterion for startingthe engine, the clutch having a disengaged state operable to decouplethe engine from the motor and an engaged state operable to couple theengine to the motor, and the clutch may be operably configured to changefrom the disengaged state to the engaged state in response to the clutchcontrol signal.

The provisions for producing the clutch control signal may includeprovisions for producing a discrete clutch control signal having firstand second states, the clutch being operably configured to change fromthe disengaged State to the engaged state in response to the clutchcontrol signal having the first state.

The provisions for producing the clutch control signal may includeprovisions for producing a clutch control signal having a time-varyingamplitude representing a desired amount of engagement of the clutchbetween the engaged state and the disengaged state, the clutch beingresponsive to the clutch control signal to control an amount of slippageof the clutch when coupling the engine to the motor.

The apparatus may include provisions for producing a transmission shiftsignal in response to the vehicle operating condition meeting thecriterion for starting the engine, and the provisions for causing theautomatic transmission to change gear ratio may include provisions forcausing the automatic transmission to change gear ratio to the targetgear ratio in response to the transmission shift signal.

The provisions for producing the clutch control signal may includeprovisions for producing the clutch control signal a first time periodafter the vehicle operating condition meets the criterion for startingthe engine, and the provisions for producing the transmission shiftsignal may include provisions for producing the transmission shiftsignal a second time period after the vehicle operating condition meetsthe criterion for starting the engine, the first and second time periodsbeing selected such that a substantially constant acceleration of thevehicle may be maintained while starting the engine.

The apparatus may include provisions for producing an engine startsignal in response to the vehicle operating condition meeting thecriterion for starting the engine.

The provisions for producing the engine start signal may includeprovisions for producing at least one of an ignition signal forcontrolling ignition of the engine, and a fuel control signal forcausing fuel to be supplied to the engine.

The provisions for producing the engine start signal may includeprovisions for producing the engine start signal a third time periodafter the vehicle operating condition meets the criterion for startingthe engine, the third time period being sufficient time to permit theengine to reach a rotational speed that generally matches the rotationalspeed of the motor.

The automatic transmission may be operably configured to provide aplurality of discrete gear ratios and the provisions for causing theautomatic transmission to change the gear ratio may include provisionsfor causing the automatic transmission to change gear ratio from a firstgear ratio to the target gear ratio.

The automatic transmission may be operably configured to provide acontinuously variable gear ratio and the provisions for causing theautomatic transmission to change the gear ratio may include provisionsfor causing the automatic transmission to change gear ratio by an amountsufficient to provide the target gear ratio between the motor and the atleast one drive wheel.

In accordance with another aspect of the invention there is provided anapparatus for starting an engine in a hybrid vehicle being driven by anelectric motor, the motor being operably configured to delivermechanical power through an automatic transmission to at least onevehicle drive wheel to cause an acceleration of the vehicle. Theapparatus includes a controller operably configured to cause the engineto be coupled to the motor to cause an inertial load on the motor thuscausing the motor to decelerate to a reduced rotational speed to providea starting torque to the engine for starting the engine, and cause theautomatic transmission to change gear ratio to a target gear ratioassociated with the reduced rotational speed while causing the motor todecelerate, the motor being operable to deliver increased torque at thereduced rotational speed, thereby generally maintaining the accelerationof the vehicle.

The controller may be operably configured to couple the engine to themotor when a vehicle operating condition meets a criterion for startingthe engine.

The controller may be operably configured to cause the automatictransmission to change gear ratio to the target gear ratio when thevehicle operating condition meets the criterion for starting the engine.

The controller may be operably configured to couple the engine to themotor when at least one of the motor speed reaches a reference speed,the vehicle reaches a reference velocity, a storage element forsupplying electrical energy to the motor reaches a reference minimumstate of charge, and a voltage at which the electrical energy may besupplied to the motor reaches a reference minimum level.

The controller may be operably configured to cause a clutch between themotor and the engine to be engaged to transmit the starting torque tothe engine.

The controller may be operably configured to produce a clutch controlsignal when a vehicle operating condition meets a criterion for startingthe engine, the clutch having a disengaged state operable to decouplethe engine from the motor and an engaged state operable to couple theengine to the motor, and the clutch may be operably configured to changefrom the disengaged state to the engaged state in response to the clutchcontrol signal.

The controller may be operably configured to produce a discrete clutchcontrol signal having first and second states, the clutch being operablyconfigured to change from the disengaged state to the engaged state inresponse to the clutch control signal having the first state.

The controller may be operably configured to produce a clutch controlsignal having a time-varying amplitude representing a desired amount ofengagement of the clutch between the engaged state and the disengagedstate, the clutch being responsive to the clutch control signal tocontrol an amount of slippage of the clutch when coupling the engine tothe motor.

The controller may be operably configured to produce a transmissionshift signal in response to the vehicle operating condition meeting thecriterion for starting the engine, and the controller may be operablyconfigured to cause the automatic transmission to change gear ratio tothe target gear ratio in response to the transmission shift signal.

The controller may be operably configured to produce the clutch controlsignal a first time period after the vehicle operating condition meetsthe criterion for starting the engine, and the controller may beoperably configured to produce the transmission shift signal a secondtime period after the vehicle operating condition meets the criterionfor starting the engine, the first and second time periods beingselected such that a substantially constant acceleration of the vehiclemay be maintained while starting the engine.

The controller may be operably configured to produce an engine startsignal in response to the vehicle operating condition meeting thecriterion for starting the engine.

The controller may be operably configured to produce at least one of anignition signal for controlling ignition of the engine, and a fuelcontrol signal for causing fuel to be supplied to the engine.

The controller may be operably configured to produce the engine startsignal a third time period after the vehicle operating condition meetsthe criterion for starting the engine, the third time period beingsufficient time to permit the engine to reach a rotational speed thatgenerally matches the rotational speed of the motor.

The automatic transmission may be operably configured to provide aplurality of discrete gear ratios and the controller may be operablyconfigured to cause the automatic transmission to change gear ratio froma first gear ratio to the target gear ratio.

The automatic transmission may be operably configured to provide acontinuously variable gear ratio and the controller may be operablyconfigured to cause the automatic transmission to change gear ratio byan amount sufficient to provide the target gear ratio between the motorand the at least one drive wheel.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate embodiments of the invention,

FIG. 1 is a schematic view of a hybrid vehicle in accordance with afirst embodiment of the invention;

FIG. 2 is a schematic view of a hybrid vehicle in accordance with asecond embodiment of the invention;

FIG. 3 is a schematic view of a processor circuit for implementing acontroller for the hybrid vehicle shown in FIG. 2;

FIG. 4 is a flowchart depicting blocks of code for carrying out a methodfor starting an engine of the hybrid vehicle shown in FIG. 2; and

FIG. 5 is a series of graphs of control signals produced by theprocessor circuit shown in FIG. 3, and a resulting motor speed, enginespeed, and vehicle speed.

DETAILED DESCRIPTION

Referring to FIG. 1, a hybrid vehicle according to a first embodiment ofthe invention is shown generally at 10. The hybrid vehicle 10 includesan electric motor 12, an engine 14, an automatic transmission 16, and apair of drive wheels 18.

The automatic transmission 16 is mechanically coupled to the drivewheels 18 through a transmission output shaft 17, a differential 19, anda drive axle 21. The automatic transmission 16 includes an interface 20having an input 22 for receiving a shift signal for causing theautomatic transmission to change gear ratio. The automatic transmission16 may comprise a conventional automatic transmission having a pluralityof gears (not shown), which may be configured to provide a plurality ofdiscrete gear ratios between the first shaft 24 and the transmissionoutput shaft 17. Alternatively, the automatic transmission 16 mayinclude a continuously variable transmission that is responsive theshift signal to provide gear ratios within a range of gear ratios thatthe automatic transmission is capable of producing. In other embodimentsthe automatic transmission 16 may comprise an auto-shifted manualtransmission, which includes a gear configuration similar toconventional manual transmissions, but further includes an automaticclutch and actuators for automatically shifting gear configuration.

The motor 12 is mechanically coupled to the automatic transmission 16 bya first shaft 24, which couples mechanical power generated by the motor12 to the automatic transmission for driving the wheels 18 of thevehicle. The motor 12 may comprise an alternating current (AC) inductionmotor, a brushless direct current (DC) motor, or any other electricmotor suitable for driving the vehicle 10.

The motor 12 includes an interface 26, which is electrically coupled toan energy bus 32 for receiving electrical energy to generate themechanical power at the first shaft 24. The interface 26 also includesan input 28 for receiving a motor control signal for controlling anamount of power generated by the motor 12.

The hybrid vehicle 10 further includes an energy storage element 30,which is electrically coupled to the energy bus 32, for providingelectrical energy to the motor in order to generate mechanical power.The storage element may include a plurality of battery cells, such asnickel metal hydride cells. Alternatively the storage element mayinclude an ultra-capacitor, or a combination of battery cells and anultra-capacitor, for example.

In general, the storage element produces a direct current (DC) on theenergy bus 32. The interface 26 of the motor 12 receives the DC currentand controls a current and/or voltage supplied to the motor in responseto the motor control signal received at the input 28 to cause the motorto generate mechanical power at the first shaft 24 at a suitable torqueand rotational speed for operating the vehicle.

In embodiments where the motor 12 is an AC induction motor or abrushless DC motor, the interface 26 may include an inverter forconverting the direct current produced by the storage element 30 into analternating current suitable for driving such motors.

The motor 12 is also mechanically coupled to a second shaft 34. Ingeneral the motor includes a rotor element (not shown), which hasmechanical couplings (not shown) at each end for coupling to the firstshaft 24 and to the second shaft 34, such that the rotor, the firstshaft, and the second shaft all rotate together as a unit.

The engine 14 is mechanically coupled to a third shaft 40, and isoperable to generate a torque on the third shaft by combustion of a fuelsource (not shown). The engine 14 may be any type of internal orexternal combustion engine, e.g. Otto, Atkinson, and diesel cycleengines, Stirling engines, gas turbine engines, etc. The engine 14 mayrun on a fuel such as gasoline, diesel, biogas, or other bio-fuelsincluding cellulosic and other ethanols, propane etc.

The engine 14 includes an interface 36 having an input 38 for receivingan engine start signal, for causing the engine to start. Depending onthe type of engine 14, the start signal may include a plurality ofsignals. For example, in a gasoline engine, the start signal may includea fuel signal for controlling fuel delivered to the engine, and anignition signal for causing firing of spark plugs.

In the embodiment shown, the hybrid vehicle 10 also includes a clutch 42for mechanically coupling torque from the engine 14 to the second shaft34, or from the second shaft to the engine. The clutch 42 includes afirst friction disk 44, which is mechanically coupled to the third shaft40, and the second friction disk 46, which is mechanically coupled tothe motor 12 by the second shaft 34. The clutch 42 is engaged by causingthe friction disks 44 and 46 to be brought into contact with each other,and the clutch is disengaged by causing the friction disks to beseparated (as shown in FIG. 1).

The clutch 42 also includes an input 48 for receiving a clutch controlsignal for controlling a state of engagement of the clutch. The clutchcontrol signal may have two states, including a first state representingan engaged state of the clutch, and a second state representing adisengaged state of the clutch. Alternatively, the clutch control signalmay have time-varying amplitude values representing an instantaneousdesired amount of engagement of the clutch between a fully engaged stateand a fully disengaged state, such that the clutch 42 may be engaged insuch a manner as to control an amount of slippage when mechanicallycoupling the engine 14 to the motor 12.

In the embodiment shown in FIG. 1, the clutch 42 includes two frictiondisks 44 and 46, however in other embodiments (not shown) the clutch mayinclude a plurality of interleaved friction disks having increased areaof contact between the disks for transmitting higher torque.

In some embodiments the motor 12 may be capable of operating in agenerator mode, in which case the motor receives a torque on the firstshaft 24 or on the second shaft 34, and produces electrical energy onthe energy bus 32 for charging the storage element 30. The torque forproducing electrical energy in the generator mode may be produced whenthe vehicle 10 is maintaining or reducing speed, in which case thekinetic energy of the vehicle is transferred to the drive wheels 18acting on a road surface, through the automatic transmission 16, and tothe first shaft 24. Alternatively, the torque for producing electricalenergy in the generator mode may be produced by the engine andtransferred through the clutch 42 (when the clutch is engaged) to thesecond shaft 34.

The hybrid vehicle 10 further includes a controller 50 for controllingstarting of the engine 14. The controller 50 has a first output 52 forproducing the motor control signal, a second output 54 for producing theshift signal, a third output 56 for producing the clutch control signal,and a fourth output 58 for producing the engine start signal.

In the embodiment shown in FIG. 1, the hybrid vehicle 10 is shown ashaving a pair of drive wheels 18. However, it should be readilyappreciated that in other embodiments, drive power may be coupled to allfour wheels (or more wheels if provided), or to a single wheel (in thecase of a motorcycle or three-wheeled vehicle, for example).

Referring to FIG. 2, a second embodiment of a hybrid vehicle is showngenerally at 80. The hybrid vehicle 80 includes the motor 12, the engine14, the automatic transmission 16, and the energy storage element 30,generally as shown in FIG. 1.

The motor 12, in this embodiment, further includes a speed sensor 82having an output 84 for producing a motor speed signal (S_(m))representing a rotational speed of the motor.

The engine 14 further includes a speed sensor 86 having an output 88 forproducing an engine speed signal (S_(e)) representing a rotational speedof the engine.

The hybrid vehicle 80 further includes a velocity sensor 90 having anoutput 92 for producing a vehicle velocity signal representing avelocity of the vehicle. In general the velocity sensor 90 may bemechanically, optically, or magnetically coupled to the axle 21 or oneof the drive wheels 18 and the velocity sensor 90 may further includecircuitry for converting a sensed rotational speed of the wheels 18 oraxle 21 into a vehicle velocity signal. Alternatively, the velocitysensor 90 may be mechanically, optically, or magnetically coupled to thetransmission output shaft 17.

The hybrid vehicle 80 further includes an operator input device 94having an output 96 for producing a demand signal. The operator inputdevice 94 may include a foot pedal disposed in a driving compartment(not shown) of the hybrid vehicle 80, which is configured to produce thedemand signal in response to an operator depressing the pedal, forexample.

In this embodiment, the storage element 30 includes an output 31 forproducing a state of charge (SOC) signal representing a charge level ofthe storage element.

The hybrid vehicle 80 also includes a controller 100, which in thisembodiment includes a first input 102 for receiving the demand signal, asecond input 104 for receiving the velocity signal, a third input 106for receiving the motor speed signal S_(m), a fourth input 108 forreceiving the engine speed signal S_(e), and a fifth input 111 forreceiving the state of charge signal from the storage element 30.

The controller 100 also includes a first output 110 for producing theshift signal, a second output 112 for producing the motor controlsignal, a third output 114 for producing the engine start signal, and afourth output 116 for producing the clutch control signal.

Referring to FIG. 3, in one embodiment the controller 100 may beimplemented using a processor circuit shown generally at 130. Theprocessor circuit 130 includes a microprocessor 132, a program memory134, a variable memory 136, a parameter memory 138, a media reader 140,and an input output port (I/O) 142, all of which are in communicationwith the microprocessor 132.

The I/O 142 includes the first input 102 for receiving the demandsignal, the second input 104 for receiving the vehicle velocity signal,the third input 106 for receiving the motor speed signal, the fourthinput 108 for receiving the engine speed signal, and the fifth input forreceiving the state of charge signal from the storage element 30. TheI/O 142 further includes the first output 110 for producing the shiftsignal, the second output 112 for producing the motor control signal,the third output 114 for producing the start signal, and the fourthoutput 116 for producing the clutch control signal.

Program codes for directing the microprocessor 132 to carry out variousfunctions are stored in the program memory 134, which may be implementedas a random access memory (RAM) and/or a hard disk drive (HDD), or acombination thereof.

The media reader 140 facilitates loading program codes into the programmemory 134 from a computer readable medium 144, such as a CD ROM disk146, or a computer readable signal 148, such as may be received over anetwork such as a controller area network (CAN), which may beimplemented in the vehicle, for example.

The variable memory 136 includes a plurality of storage locationsincluding a store 150 for storing a value of the demand signal, a store152 for storing a value of the vehicle velocity signal, a store 154 forstoring a value of the motor speed S_(m), and a store 156 for storing avalue of the engine speed signal S_(e). The variable memory 136 may beimplemented in random access memory, for example.

The parameter memory 138 includes a plurality of storage locations,including a store 160 for storing values representing vehicle operatinglimits, a store 162 for storing engine start criteria, a store 164 forstoring a value of a loop interval time, and stores 166, 168, and 170for storing values of reference delay times D1, D2, and D3. Theparameter memory 138 may be implemented in random access memory, forexample.

In other embodiments (not shown), the controller 100 may be partly orfully implemented using a hardware logic circuit including discretelogic circuits and/or an application specific integrated circuit (ASIC).

Referring to FIG. 1, operating power for driving the vehicle 10 issupplied to the drive wheels 18 through the automatic transmission 16.When the clutch control signal is in the disengaged state, the clutch 42decouples the engine from the second shaft 34. The motor 12 receiveselectrical energy from the storage element 30 on the energy bus 32, andthe motor generates mechanical power which is mechanically coupled tothe transmission 16 by the first shaft 24. Advantageously, when theclutch 42 is in the disengaged state, the engine 14 is stopped to reducefuel consumption and to curtail emissions of pollutants due tocombustion of fuel.

In general, the controller 50 is operably configured to produce a motorcontrol signal at the first output 52, which causes the motor 12 togenerate mechanical power at a suitable torque and rotational speed foraccelerating the vehicle 10.

The controller 50 is further configured to cause the engine 14 to bemechanically coupled to the motor 12 by producing a clutch controlsignal at the second output 56. The clutch control signal causes theclutch 42 to couple the engine 14 to the motor 12 such that the motor isdecelerated from a first rotational speed to a second rotational speed.The deceleration of the motor 12 is operable to generate a startingtorque for starting the engine 14.

The controller 50 also produces a transmission shift signal at thesecond output 54 for causing the automatic transmission 16 to changegear ratio from a first gear ratio to a second gear ratio while themotor 12 is being decelerated. The motor 12 generates increased torqueat the second rotational speed such that the mechanical power coupled tothe drive wheels 18 at the second gear ratio remains generally constantwhile starting the engine 14, thus maintaining the acceleration of thevehicle 10.

The controller 50 also produces an engine start signal at the fourthoutput 58 for starting the engine 14 when the torque received from thedecelerating motor causes the engine to reach sufficient rotationalspeed for starting the engine.

The operation of the hybrid vehicle is described in greater detail withreference to FIGS. 2-5.

Referring to FIG. 4, a flowchart depicting blocks of code for directingthe processor circuit 130 to cause the engine 14 to be started is showngenerally at 200. The process 200 starts with the clutch 42 in thedisengaged state, the engine 14 stopped, and the vehicle 80 in astationary state or moving at a low velocity. The blocks generallyrepresent codes that may be read from the computer readable medium 144,and stored in the program memory 134, for directing the microprocessor132 to perform various functions related to starting the engine 14. Theactual code to implement each block may be written in any suitableprogram language, such as C, C++, and/or assembly code, for example.

A first block of codes 202 directs the microprocessor 132 to cause theI/O 142 to receive the demand signal from the operator input device 94at the first input 102 and to store a value of the demand signal in thestore 150 of the variable memory 136.

Block 204 directs the microprocessor 132 to cause the I/O to receive thevelocity signal at the second input 104 and to store a value of thevelocity signal in the store 152 of the variable memory 136.

Block 206 directs the microprocessor 132 to cause the I/O 142 to readthe velocity value from the store 152, and to produce the shift signalat the first output 110, having a state representing a first gear ratioof the automatic transmission 16 suitable for accelerating the vehiclefrom the current vehicle velocity. The automatic transmission 16receives the shift signal at the input 22 of the interface 20 andresponds by configuring the transmission to provide the first gearratio. In embodiments where the automatic transmission 16 is aconventional automatic transmission, the transmission includes aplurality of electrical solenoids which are activated by the interface20 to configure the gears to produce a desired gear ratio, for example.

Block 208 then directs the microprocessor 132 to read the demand signalvalue from the store 150, and the vehicle operating limits from thestore 160, and to compute a motor control signal value. The motorcontrol signal value represents a torque demand within the safeoperating limits for the vehicle 80 and the motor 12 that will at leastpartially satisfy the operator demand. The operating limits may include,for example, a current state of charge of the storage element 30, amaximum motor current, maximum motor torque, etc. Block 206 then directsthe microprocessor 132 to produce a motor demand signal at the secondoutput 112.

The motor demand signal is received at the input 28 of the motorinterface 26, and the interface causes the motor 12 to generate a torquein response by causing electrical energy from the storage element 30 tobe supplied to the motor on the energy bus 32. The torque ismechanically coupled through the first shaft 24, through thetransmission 16, and to the drive wheels 18, thus causing the vehicle 80to accelerate.

Block 209 then directs the microprocessor 132 to cause the motor speedsignal S_(m) to be received at the third input 106, and stored in thestore 154 of the variable memory 136, and the engine speed signal S_(e)to be received at the fourth input 108, and stored in the store 156 ofthe variable memory 136.

Block 210 then directs the microprocessor 132 to read the vehiclevelocity v from the store 152, and the motor speed S_(m) from the store154, and the engine speed S_(e) from the store 156, and to compare v,S_(m), and S_(e) to the engine start criteria stored in the store 162 inthe parameter memory 138. The engine start criteria may be expressedfollows:

Engine Start Criteria=f(v,S _(m) ,S _(e) Other Operating Conditions)  Eqn 1

where other operating conditions may include operating conditions suchas a fuel economy target, a voltage on the energy bus 32, and storageelement state of charge, for example.

If at block 210, the vehicle operating condition does not meet theengine start criteria, then the process continues at block 212, whichdirects the microprocessor 132 to read the loop interval time from thestore 164 in the parameter memory 138 and to wait until the loopinterval time expires before returning to block 202. Blocks 202 to 210are thus repeated at a fixed time interval equal to the loop intervaltime. For example, the loop time interval may be 10 milliseconds and theblocks 202 to 210 may be executed in 5 milliseconds in which case thewait time at block 212 is 5 milliseconds such that the process returnsto block 202 every 10 milliseconds until the condition at block 210 ismet. At each repetition of block 202, the demand signal from theoperator input device 94 may have changed, which may cause a change inthe motor control signal at block 208. In some embodiments, whenaccelerating the vehicle, the processor circuit 130 may cause thetransmission 16 to change gear ratio even though the operating conditionhas not been met at block 210. In such cases the transmission 16 will beconfigured to provide a second gear ratio for continuing acceleration ofthe vehicle. In general, the transmission 16 may be caused to changegear ratio several times before the vehicle operating condition meetsthe criterion, depending on the size of the vehicle 80 and the numbergear ratios provided by the transmission 16.

If at block 210, the vehicle operating condition meets the engine startcriteria then the process continues at blocks 214, 216, and 218, whichoptionally direct the microprocessor 132 to read the reference delaytimes “D1”, “D2”, and “D3” from the stores 166, 168, and 170respectively, and to wait for a period of time equal to the respectivedelay times, before the process continues at blocks 220, 222, and 224respectively. Accordingly, blocks 220, 222, and 224 may be executedsimultaneously if the reference delays D1, D2, and D3 are equal or setto zero. Alternatively if the reference delays D1, D2, and D3 havedifferent values, the blocks 220, 222, and 224 may be executed at timesthat are staggered in time with respect to each other. In general thedelays D1, D2, and D3 will be dependent on a latency time betweenproducing the clutch, shift and engine start control signals and therespective actions taking place. The delays D1, D2, and D3 may furtherbe dependent on a desired delay between the respective actions to causean even acceleration of the vehicle 80 while starting the engine 14, forexample.

Block 220 directs the microprocessor 132 to cause the I/O 142 to producethe clutch control signal at the output 116, to cause the engine 14 tobe mechanically coupled to the second shaft 34 and thus to the motor 12.The engine 14 loads the motor 12 causing it to decelerate from a firstrotational speed to a second rotational speed due to the increasedinertial load imposed by the engine. The deceleration causes rotationalkinetic energy of the motor 12 to be coupled into through the clutch 42to the engine for starting the engine. The torque available may becalculated from the following relation:

τ_(s)=Iα  Eqn 2

where τ_(s) is the torque available for starting the engine, I is theinertia of the rotating mass of the motor 12 (i.e. the mass of rotor andcoupled shafts), and α is the rotational deceleration of the motor whenmechanically coupling the engine 14 to the motor.

While the motor 12 is decelerating, block 222 directs the microprocessor132 to cause the I/O 142 to produce the shift signal at the first output110 to cause the transmission 16 to change gear ratio from the firstgear ratio to a second gear ratio. In general, an electric motor, suchas the motor 12, is capable of producing greatest torque at lowerrotational speeds, and thus the change in gear ratio causes increasedgeneration of torque by the motor at the second rotational speed of themotor. In general, when a constant electrical power is being supplied tothe motor 12, the mechanical power produced will also be substantiallyconstant. The mechanical power may be written as:

P_(m)=τ_(d)S_(m)   Eqn 3

where P_(m) is the mechanical power supplied to the first shaft 24 (andhence to the drive wheels 18 through the transmission 16), τ_(d) is thetorque on the first shaft 24, and s_(m) is the rotational speed of themotor.

Block 224 directs the microprocessor 132 to cause the I/O 142 to producethe engine start signal at the third output 114 to cause the engine 14to receive fuel and/or an ignition signal such that when the engine isrotated by the torque provided by the motor 12 on the third shaft 40,the engine is started.

Advantageously, the gear ratio change may be selected to causesufficient increased torque generation by the motor 12 to cause thevehicle to continue to accelerate smoothly, or to only experience asimilar change in acceleration that would result from a gear shift inabsence of starting the engine 14.

FIG. 5 shows a series of graphical views illustrating the effect of thedelays D1, D2, and D3 shown in blocks 214, 216, and 218. Referring toFIG. 5, a first graph 250 depicts values of the clutch, shift and startcontrol signals vs. time. A second graph 252 depicts motor speed vs.time. A third graph 254 depicts engine speed vs. time. A fourth graph256 depicts the velocity of the vehicle 80 vs. time. The graphs 250,252, 254, and 256 share a common time axis 258.

As depicted on the graph 252, the motor speed increases from zero to arotational speed S_(m1) between time t₀ and time t_(c). As shown ongraph 256, the vehicle 80 experiences a corresponding velocity increasebetween the time t₀ and t_(c).

During the time interval from t₀ to t_(c), the graph 250 shows the shiftsignal value at first state for configuring the automatic transmission16 to provide a first gear ratio.

At the time t_(c), the vehicle operating conditions meet the enginestart criteria. At a time t₁ (corresponding to a delay time D1 from thetime t_(c)), the clutch control signal changes state from a first level,to a second level between the disengaged state and the fully engagedstate. While the clutch signal is changing, some slippage of the clutchoccurs to cause the engine speed shown in graph 254 to begin toincrease.

The motor decelerates between times t₁ and t₂ as the torque beingproduced by the motor 12 is mechanically coupled to the engine throughthe clutch 42, which may result in a slight decrease in vehicle speed asshown on graph 256 between times t₁ and t₂.

At a time t₂ (corresponding to a delay time D2 from the time t_(c)) theshift signal changes state, causing the gear ratio of the transmission16 to be changed such that the motor speed decreases, as shown in graph252 between the times t₂ and t₃, resulting in increased torquegeneration by the motor 12.

The engine speed shown in graph 254 is at zero (i.e. the engine isstopped) between times t₀ and t₁. At time t₁ the clutch 42 is engaged tomechanically couple the engine 14 to the second shaft 34 and the enginerotational speed begins to increase. However, in this embodiment, theengine start signal is not produced until a time t₃, which allows thespeed of the engine 14 to be substantially matched to the speed of themotor 12 before starting the engine. Once started (at the time t₃) theengine 14 provides torque through the third shaft 40 and the clutch 42to the second shaft 34, and the vehicle continues accelerating as shownin graph 256.

In the embodiment shown in FIG. 5, the delay times D1, D2, and D3 aregenerally selected to minimize the effect on vehicle speed as shown ingraph 256, where the vehicle speed generally increases steadily, exceptfor a small speed disturbance between times t₁ and t₃. The delay timesD1, D2, and D3 may also be used to account for the latency time betweenproducing the clutch, shift, and engine start signals and the respectiveactions occurring.

In other embodiments the clutch, shift and start signals may besynchronized to change state simultaneously, such that the offsettingchanges are all initiated together.

Advantageously, the electric motor 12 is most efficient when supplying atorque a low rotational speed, while the engine 14 is most efficient athigher rotational speed, and accordingly, when the vehicle 80 isaccelerating from a stationary state, or operating at low vehiclevelocity, the engine 14 may be inactive (i.e. not started).Advantageously, the engine 14 is only started when the vehicle operationmeets the operating criterion at the time t_(c), thus minimizing fuelconsumption when operating the vehicle at low velocity or understart/stop driving conditions. Furthermore, by causing a transmissiongear change while mechanically coupling the engine 14 to the motor 12,significant changes in vehicle acceleration when starting the engine areprevented.

While specific embodiments of the invention have been described andillustrated, such embodiments should be considered illustrative of theinvention only and not as limiting the invention as construed inaccordance with the accompanying claims.

1. A method for starting an engine in a hybrid vehicle being driven byan electric motor, the motor being operably configured to delivermechanical power through an automatic transmission to at least onevehicle drive wheel to cause an acceleration of the vehicle, the methodcomprising: coupling the engine to the motor to cause an inertial loadon the motor thus causing the motor to decelerate to a reducedrotational speed to provide a starting torque to the engine for startingthe engine; and causing the automatic transmission to change gear ratioto a target gear ratio associated with said reduced rotational speedwhile causing the motor to decelerate, the motor being operable todeliver increased torque at said reduced rotational speed, therebygenerally maintaining the acceleration of the vehicle.
 2. The method ofclaim 1 wherein coupling the engine comprises coupling the engine to themotor when a vehicle operating condition meets a criterion for startingthe engine.
 3. The method of claim 2 wherein causing the automatictransmission to change gear ratio comprises causing the automatictransmission to change gear ratio to said target gear ratio when saidvehicle operating condition meets said criterion for starting theengine.
 4. The method of claim 2 wherein coupling the engine to themotor when said vehicle operating condition meets said criterion forstarting the engine comprises coupling the engine to the motor when atleast one of: the motor speed reaches a reference speed; the vehiclereaches a reference velocity; a storage element for supplying electricalenergy to the motor reaches a reference minimum state of charge; and avoltage at which said electrical energy is supplied to the motor reachesa reference minimum level.
 5. The method of claim 1 wherein causing theengine to be mechanically coupled to the motor comprises causing aclutch between the motor and the engine to be engaged to transmit saidstarting torque to the engine.
 6. The method of claim 5 furthercomprising producing a clutch control signal when a vehicle operatingcondition meets a criterion for starting the engine, said clutch havinga disengaged state operable to decouple the engine from the motor and anengaged state operable to couple the engine is to the motor, and whereinsaid clutch is operably configured to change from said disengaged stateto said engaged state in response to said clutch control signal.
 7. Themethod of claim 6 wherein producing said clutch control signal comprisesproducing a discrete clutch control signal having first and secondstates, said clutch being operably configured to change from saiddisengaged state to said engaged state in response to said clutchcontrol signal having said first state.
 8. The method of claim 6 whereinproducing said clutch control signal comprises producing a clutchcontrol signal having a time-varying amplitude representing a desiredamount of engagement of said clutch between said engaged state and saiddisengaged state, said clutch being responsive to said clutch controlsignal to control an amount of slippage of said clutch when coupling theengine to the motor.
 9. The method of claim 6 further comprisingproducing a transmission shift signal in response to said vehicleoperating condition meeting said criterion for starting the engine, andwherein causing the automatic transmission to change gear ratiocomprises causing the automatic transmission to change gear ratio tosaid target gear ratio in response to said transmission shift signal.10. The method of claim 9 wherein producing said clutch control signalcomprises producing said clutch control signal a first time period aftersaid vehicle operating condition meets said criterion for starting theengine, and wherein producing said transmission shift signal comprisesproducing said transmission shift signal a second time period after saidvehicle operating condition meets said criterion for starting theengine, said first and second time periods being selected such that asubstantially constant acceleration of the vehicle is maintained whilestarting the engine.
 11. The method of claim 2 further comprisingproducing an engine start signal in response to said vehicle operatingcondition meeting said criterion for starting the engine.
 12. The methodof claim 11 wherein producing said engine start signal comprisesproducing at least one of: an ignition signal for controlling ignitionof the engine; and a fuel control signal for causing fuel to be suppliedto the engine.
 13. The method of claim 11 wherein producing said enginestart signal comprises producing said engine start signal a third timeperiod after said vehicle operating condition meets said criterion forstarting the engine, said third time period being sufficient time topermit the engine to reach a rotational speed that generally matches therotational speed of the motor.
 14. The method of claim 1 wherein theautomatic transmission is operably configured to provide a plurality ofdiscrete gear ratios and wherein causing the automatic transmission tochange said gear ratio comprises causing the automatic transmission tochange gear ratio from a first gear ratio to said target gear ratio. 15.The method of claim 1 wherein the automatic transmission is operablyconfigured to provide a continuously variable gear ratio and whereincausing the automatic transmission to change said gear ratio comprisescausing the automatic transmission to change gear ratio by an amountsufficient to provide said target gear ratio between the motor and theat least one drive wheel.
 16. An apparatus for starting an engine in ahybrid vehicle being driven by an electric motor, the motor beingoperably configured to deliver mechanical power through an automatictransmission to at least one vehicle drive wheel to cause anacceleration of the vehicle, the apparatus comprising: means forcoupling the engine to the motor to cause an inertial load on the motorthus causing the motor to decelerate to a reduced rotational speed toprovide a starting torque to the engine for starting the engine; andmeans for causing the automatic transmission to change gear ratio to atarget gear ratio associated with said reduced rotational speed whilecausing the motor to decelerate, the motor being operable to deliverincreased torque at said reduced rotational speed, thereby generallymaintaining the acceleration of the vehicle.
 17. The apparatus of claim16 wherein said means for coupling the engine comprises means forcoupling the engine to the motor when a vehicle operating conditionmeets a criterion for starting the engine.
 18. The apparatus of claim 17wherein said means for causing the automatic transmission to change gearratio comprises means for causing the automatic transmission to changegear ratio to said target gear ratio when said vehicle operatingcondition meets said criterion for starting the engine.
 19. Theapparatus of claim 17 wherein said means for coupling the engine to themotor when said vehicle operating condition meets said criterion forstarting the engine comprises means for coupling the engine to the motorwhen at least one of: the motor speed reaches a reference speed; thevehicle reaches a reference velocity; a storage element for supplyingelectrical energy to the motor reaches a reference minimum state ofcharge; and a voltage at which said electrical energy is supplied to themotor reaches a reference minimum level.
 20. The apparatus of claim 16wherein said means for causing the engine to be mechanically coupled tothe motor comprises causing a clutch between the motor and the engine tobe engaged to transmit said starting torque to the engine.
 21. Theapparatus of claim 20 further comprising means for producing a clutchcontrol signal when a vehicle operating condition meets a criterion forstarting the engine, said clutch having a disengaged state operable todecouple the engine from the motor and an engaged state operable tocouple the engine is to the motor, and wherein said clutch is operablyconfigured to change from said disengaged state to said engaged state inresponse to said clutch control signal.
 22. The apparatus of claim 21wherein said means for producing said clutch control signal comprisesmeans for producing a discrete clutch control signal having first andsecond states, said clutch being operably configured to change from saiddisengaged state to said engaged state in response to said clutchcontrol signal having said first state.
 23. The apparatus of claim 21wherein said means for producing said clutch control signal comprisesmeans for producing a clutch control signal having a time-varyingamplitude representing a desired amount of engagement of said clutchbetween said engaged state and said disengaged state, said clutch beingresponsive to said clutch control signal to control an amount ofslippage of said clutch when coupling the engine to the motor.
 24. Theapparatus of claim 21 further comprising means for producing atransmission shift signal in response to said vehicle operatingcondition meeting said criterion for starting the engine, and whereinsaid means for causing the automatic transmission to change gear ratiocomprises means for causing the automatic transmission to change gearratio to said target gear ratio in response to said transmission shiftsignal.
 25. The apparatus of claim 24 wherein said means for producingsaid clutch control signal comprises means for producing said clutchcontrol signal a first time period after said vehicle operatingcondition meets said criterion for starting the engine, and wherein saidmeans for producing said transmission shift signal comprises means forproducing said transmission shift signal a second time period after saidvehicle operating condition meets said criterion for starting theengine, said first and second time periods being selected such that asubstantially constant acceleration of the vehicle is maintained whilestarting the engine.
 26. The apparatus of claim 17 further comprisingmeans for producing an engine start signal in response to said vehicleoperating condition meeting said criterion for starting the engine. 27.The apparatus of claim 26 wherein said means for producing said enginestart signal comprises means for producing at least one of: an ignitionsignal for controlling ignition of the engine; and a fuel control signalfor causing fuel to be supplied to the engine.
 28. The apparatus ofclaim 26 wherein said means for producing said engine start signalcomprises means for producing said engine start signal a third timeperiod after said vehicle operating condition meets said criterion forstarting the engine, said third time period being sufficient time topermit the engine to reach a rotational speed that generally matches therotational speed of the motor.
 29. The apparatus of claim 16 wherein theautomatic transmission is operably configured to provide a plurality ofdiscrete gear ratios and wherein said means for causing the automatictransmission to change said gear ratio comprises means for causing theautomatic transmission to change gear ratio from a first gear ratio tosaid target gear ratio.
 30. The apparatus of claim 16 wherein theautomatic transmission is operably configured to provide a continuouslyvariable gear ratio and wherein said means for causing the automatictransmission to change said gear ratio comprises means for causing theautomatic transmission to change gear ratio by an amount sufficient toprovide said target gear ratio between the motor and the at least onedrive wheel.
 31. An apparatus for starting an engine in a hybrid vehiclebeing driven by an electric motor, the motor being operably configuredto deliver mechanical power through an automatic transmission to atleast one vehicle drive wheel to cause an acceleration of the vehicle,the apparatus comprising a controller operably configured to: cause theengine to be coupled to the motor to cause an inertial load on the motorthus causing the motor to decelerate to a reduced rotational speed toprovide a starting torque to the engine for starting the engine; andcause the automatic transmission to change gear ratio to a target gearratio associated with said reduced rotational speed while causing themotor to decelerate, the motor being operable to deliver increasedtorque at said reduced rotational speed, thereby generally maintainingthe acceleration of the vehicle.
 32. The apparatus of claim 31 whereinsaid controller is operably configured to couple the engine to the motorwhen a vehicle operating condition meets a criterion for starting theengine.
 33. The apparatus of claim 32 wherein said controller isoperably configured to cause the automatic transmission to change gearratio to said target gear ratio when said vehicle operating conditionmeets said criterion for starting the engine.
 34. The apparatus of claim32 wherein said controller is operably configured to couple the engineto the motor when at least one of: the motor speed reaches a referencespeed; the vehicle reaches a reference velocity; a storage element forsupplying electrical energy to the motor reaches a reference minimumstate of charge; and a voltage at which said electrical energy issupplied to the motor reaches a reference minimum level.
 35. Theapparatus of claim 31 wherein said controller is operably configured tocause a clutch between the motor and the engine to be engaged totransmit said starting torque to the engine.
 36. The apparatus of claim35 wherein said controller is operably configured to produce a clutchcontrol signal when a vehicle operating condition meets a criterion forstarting the engine, said clutch having a disengaged state operable todecouple the engine from the motor and an engaged state operable tocouple the engine is to the motor, and wherein said clutch is operablyconfigured to change from said disengaged state to said engaged state inresponse to said clutch control signal.
 37. The apparatus of claim 36wherein said controller is operably configured to produce a discreteclutch control signal having first and second states, said clutch beingoperably configured to change from said disengaged state to said engagedstate in response to said clutch control signal having said first state.38. The apparatus of claim 36 wherein said controller is operablyconfigured to produce a clutch control signal having a time-varyingamplitude representing a desired amount of engagement of said clutchbetween said engaged state and said disengaged state, said clutch beingresponsive to said clutch control signal to control an amount ofslippage of said clutch when coupling the engine to the motor.
 39. Theapparatus of claim 36 wherein said controller is operably configured toproduce a transmission shift signal in response to said vehicleoperating condition meeting said criterion for starting the engine, andwherein said controller is operably configured to cause the automatictransmission to change gear ratio to said target gear ratio in responseto said transmission shift signal.
 40. The apparatus of claim 39 whereinsaid controller is operably configured to produce said clutch controlsignal a first time period after said vehicle operating condition meetssaid criterion for starting the engine, and wherein said controller isoperably configured to produce said transmission shift signal a secondtime period after said vehicle operating condition meets said criterionfor starting the engine, said first and second time periods beingselected such that a substantially constant acceleration of the vehicleis maintained while starting the engine.
 41. The apparatus of claim 32wherein said controller is operably configured to produce an enginestart signal in response to said vehicle operating condition meetingsaid criterion for starting the engine.
 42. The apparatus of claim 41wherein said controller is operably configured to produce at least oneof: an ignition signal for controlling ignition of the engine; and afuel control signal for causing fuel to be supplied to the engine. 43.The apparatus of claim 41 wherein said controller is operably configuredto produce said engine start signal a third time period after saidvehicle operating condition meets said criterion for starting theengine, said third time period being sufficient time to permit theengine to reach a rotational speed that generally matches the rotationalspeed of the motor.
 44. The apparatus of claim 31 wherein the automatictransmission is operably configured to provide a plurality of discretegear ratios and wherein said controller is operably configured to causethe automatic transmission to change gear ratio from a first gear ratioto said target gear ratio.
 45. The apparatus of claim 31 wherein theautomatic transmission is operably configured to provide a continuouslyvariable gear ratio and wherein said controller is operably configuredto cause the automatic transmission to change gear ratio by an amountsufficient to provide said target gear ratio between the motor and theat least one drive wheel.